The lymphokines are a group of polypeptides belonging to the family of cytokines, i.e. hormone-like molecules that can affect various cell functions and enable communication between different cells. Recent developments have helped to clarify the role of lymphokines in the immune response. Lymphokine production by helper CD4.sup.+ (and also in CD8.sup.+) T cells frequently fall into one of two phenotypes, Th1 and Th2, in both murine and human systems (Romagnani, 1991, Immunol Today 12:256-257, Mosmann, 1989, Annu Rev Immunol, 7:145-173). Th1 cells produce interleukin 2 (IL-2), tumor necrosis factor (TNF.alpha.) and interferon gamma (IFN.gamma.) and they are responsible primarily for cell-mediated immunity such as delayed type hypersensitivity. Th2 cells produce interleukins, IL4, IL-5, IL-6, IL-9, IL-10 and IL-13 and are primarily involved in providing optimal help for humoral immune responses such as IgE and IgG4 antibody isotype switching (Mosmann, 1989, Annu Rev Immunol, 7:145-173).
Strongly polarized Th1 and Th2 responses not only play different roles in protection, they can promote different immunopathological reactions. Th1-type responses are involved organ specific autoimmunity such as experimental autoimmune uveoretinitis (Dubey et al, 1991, Eur Cytokine Network 2:147-152), experimental autoimmune encephalitis (EAE) (Beraud et al, 1991, Cell Immunol 133:379-389) and insulin dependent diabetes mellitus (Hahn et al, 1987, Eur J Immunol 18:2037-2042), in contact dermatitis (Kapsenberg et al, Immunol Today 12:392-395), and in some chronic inflammatory disorders. In contrast Th2-type responses are responsible for triggering allergic atopic disorders (against common environmental allergens) such as allergic asthma (Walker et al, 1992, Am Rev Resp Dis 148:109-115) and atopic dermatitis (van der Heijden et al, 1991, J Invest Derm 97:389-394), are thought to exacerbate infection with tissue-dwelling protozoa such as helminths (Finkelman et al, 1991, Immunoparasitol Today 12:A62-66) and Leishmania major (Caceres-Dittmar et al, 1993, Clin Exp Immunol 91:500-505), are preferentially induced in certain primary immunodeficiencies such as hyper-igE syndrome (Del Prete et al, 1989, J Clin Invest 84:1830-1835) and Omenn's syndrome (Schandene et al, 1993, Eur J Immunol 23:56-60), and are associated with reduced ability to suppress HIV replication (Barker et al, 1995, Proc Soc Nat Acad Sci USA 92:11135-11139).
Thus, it is clear that modulation of the lymphokine profiles of the is aforementioned disease states would be of therapeutic benefit. Promoting a Th1 response would most likely lead to the reversal of a Th2 phenotype and vice versa. Monoclonal antibodies (mAb) to lymphokines, lymphokines themselves and other agents such as thiol antioxidants (Jeannin et al, 1995, J Exp Med 182:1785-1792) have been shown to reverse the pathogenesis of certain diseases by inhibiting the disease-promoting cytokine pattern, either Th1 or Th2. For example, intracellular protozoan infections are limited by IFN.gamma. but exacerbated by IL4, while nematode infections are controlled by IL-4 and exacerbated by IFN.gamma. (Heinzel et al, 1989, J Exp Med 162:59-72, Else et al, 1994, J Exp Med 179:347-351). Insulin-dependent diabetes mellitus in NOD mice and EAE in mice and rats can be ameliorated by treatment with IL-4 or anti-IFN.gamma. mAb before development of the disease (Rapoport et al, 1993, J Exp Med 178:87-99, Racke et al, 1994, J Exp Med 180:1961-1966, Campbell et al, 1991, J Clin Invest 87:739-742). In addition, autoimmune graft versus host disease (GVHD) that is characterized by a systemic lupus erythrematosus-like syndrome is associated with Th2 lymphokine production and is inhibited by anti-IL-4 antibody (Umland et al, 1992, Clin Immunol Immunopathol 63:66-73). On the other hand, Th1 cytokines are produced in acute GVHD, in which donor CD8.sup.+ T cells develop into CTL and destroy the host immune system. Treatment with anti-IFN.gamma. or anti-TNF.alpha. mAb ameliorates disease, and treatment with anti-IL-2 mAb converts acute GVHD to autoimmune GVHD (Via and Finkelman, 1993, Int Immunol 5:565-572).
Clinical trials of native and recombinant IL-2 in treating HIV-infected patients have been in progress since 1983 (Volberding et al, 1987, AIDS Res Hum Retroviruses, 3:115-124). Here, the relationship comes from the fact that development of AIDS has been reported to be associated with a shift in the pattern of lymphokines produced (Clerici and Shearer, 1994, Immunol Today 15:575-581). Over time, in an infected individual progressing towards disease, a decreased expression of Th1 lymphokines such as IL-2 occurs (Maggi et al, 1987, Eur J Immunol 17:1685-1690, Gruters et al, 1990, Eur J Immunol 20:1039-1044, Clerici et al, 1993, J Clin Invest 91:759-765), concomitant with an increased production of Th2 lymphokines such as IL-4 and IL-10 (Clerici et al, 1994, J Clin Invest 93:768-775, Hoffman et al, 1985, Virology 147:326-335). T-cells from asymptomatic or long term survivors treated with IL-2 enhanced their anti-HIV activity whereas exposure to IL-4 or IL-10 reduced their ability to suppress HIV replication and to produce IL-2 (Barker et al, 1995, Proc Soc Nat Acad Sci USA 92:11135-11139).
These current immunomodulatory therapeutics (mAbs and recombinant cytokines) are, however, not without limitations. For example with chronic monoclonal antibody treatment, the host animal develops antibodies against the monoclonal antibodies thereby limiting their usefulness. `Humanized` monoclonal antibodies have been developed which apparently reduces the risk of an induced immune response to these mAbs. However, these are still under development, and in addition these new mAbs remain large proteins and therefore may have difficulty reaching there target sites. Cytokine-based therapeutics also have limitations. For example, IL-12 treatment of autoimmune GVHD leads to the development of acute GVHD in mice.
Ribavirin (1-.beta.-D-ribofuranosyl-1,2,4-triazole-3-carboxamide) is a synthetic nucleoside capable of inhibiting RNA and DNA virus replication (Huffman et al, 1973, Antimicrob. Agents Chemother 3:235, Sidwell et al, 1972, Science 177:705). We have confirmed the observations of others who suggested that ribavirin, in addition to its antiviral activity, has an effect on certain immune responses (reviewed Jolley and Suchil, 1984, Clinical Applications of Ribavirin: p93-96). We have also confirmed observations of others that ribavirin affects the proliferation of mitogen- and antigen-activated T and B lymphocytes, (Tam et at, 1995 (data not shown), Peavy et al, 1980, Infection and Immunity 29:583-589) and then when combined with cyclosporin, ribavirin showed efficacy in long term allograft survival , Jolley et al (1988, Transplantation Proc 20:703-706).
In addition, we have significantly advanced the prior research by demonstrating that ribavirin modulates the cytokine pattern of an immune response at least in part by promoting a Th1 response and suppressing a Th2 response. In hindsight, this discovery is not inconsistent with prior research. First, ribavirin is known to inhibit both functional humoral immune responses, (Peavy et al, 1981, J Immunol 126:861-864, Powers et al, 1982, Antimicrob Agents Chemother 22:108-114) and IgE-mediated modulation of mast cell secretion (Marquardt et al, 1987, J Pharmacol Exp Therapeutics 240:145-149, (both Th2 lymphokine-mediated events). Second, ribavirin antagonizes the antiviral effect of azidothymidine (AZT) in peripheral blood lymphocytes from HIV patients (Vogt et al, 1987, Science 235:1376-1379). This finding is significant because AZT decreases IL-2 receptor (IL-2R) but not IL-2 expression (Viora and Camponeschi, 1995, Cell Immunol 163:289-295). It is therefore possible that ribavirin antagonizes AZT by modulating IL-2 expression and elevating depressed levels of IL-2R. Third, ribavirin treatment of an immunocompromised patient for chronic GVHD (a Th2-mediated disorder) led to a dramatic resolution of the disease, an outcome which did not occur with conventional immunosuppressive therapies such as cyclosporin and glucocorticoids (Cassano, 1991, Bone Marrow Transplantation 7:247-248). Finally, ribavirin treatment (one year) of patients for hepatitis C (HCV) revealed fewer lymphocyte aggregates and far less liver damage than placebo controls (Dusheiko et al, 1994, Hepatology 20:206A). This observation may reflect the fact that although, the predominant immune response to hepatitis C is mediated by Th1 lymphokines, T cells of the Th0/Th2 phenotype can be infected by HCV (Zignego et al, 1994, unpublished data) and this infection may drive further antibody-mediated destruction of hepatocytes.